THE MAY-FLIES. 195 



But after all this long preparation, a few days, or 

 in most cases a few hours, will see the close of their 

 aerial existence; the perfect insects are always ex- 

 cluded in the evening, and it appears to be a general 

 rule that before the morning they have accomplished 

 the great end of their being, and vanished entirely 

 from the scene. It is to the short duration of their 

 lives in the perfect state that the name of Ephemera, 

 originally applied to all the species, refers ; and the 

 same circumstance necessitates another curious phse- 

 nomenon in their history, namely, the appearance of 

 all the specimens in a particular river at or near the 

 same time, so that for a few days they swarm in par- 

 ticular localities, and then disappear entirely until 

 the following year. During the period of their ap- 

 pearance in the perfect state they may be seen in 

 crowds in the air over the rivers, rising and falling in 

 a mazy dance, in which they are accompanied by 

 gnats and various other insects which pass their pre- 

 paratory states in water. The members of these 

 innumerable dancing parties are for the most part 

 males, at least the females are said only to join them 

 at a later hour of the evening, and their appearance, 

 when they commence their sports before the sun has 

 descended below the horizon, is said by Messrs. Kirby 

 and Spence to be indescribably gorgeous. 



But although several of our British species thus 

 appear in vast swarms for a few evenings, nothing of 

 this kind that is to be witnessed in this country can 

 at all compare with the immense flights of May-flies 

 which occur in some other parts of Europe. In 

 Holland, and some parts of Germany, the swarms of 

 one species, called Ephemera Swammerdamiana by 

 LatreHle, in honour of its first describer, are said to 



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